Kalia, your question is incomplete but let me try to clarify few things. (assuming you want to unlock as jailbreak is almost possible for all 3G and 3GS)
Jailbreak is possible foe all iOS (for iOS 5 it is just the semi-tethered one ..meaning if the phone dies or have to restart you have to connect to computer and run redsn0w)

Unlock is possible only with following  basebands
              iPhone 3G and 3GS with 04.26.08, 05.11.07, 05.12.01, 05.13.04, and 06.15.00.
              iPhone4 with 01.59.00
     (again even iOS 5 but semi-tethered)

Now if you have any of the above basebands you do not have any problem jailbreaking and unlocking. Even you have diffrent basebands you can fetch ipad baseband 6.16.00 to 3GS (running redsn0w)  but with possibility to get stuck with the BB forever and loosing GPS functionality.

If you have unlockable BB, avoid updating stock firmware from apple since that will update both iOS and baseband. To avoid that download stock IPSW file and modify with redsn0w and update via itunes. (many tutorials available ...one of the best site to go is iclarified) 

any confusion do let us know !!

good luck !